A subtotal nephrectomy in rats, the so called ablation Model leads to a progressive destruction of the kidney with manifestations of chronic renal failure. We have postulated that the progressive glomerular lesions were due to an early increase in the turnover of glomerular resident cells. This leads to an abnormal glomerular growth, with an increase in the glomerular volume detectable using morphometric measurements. We have performed autoradiographies with 3H Thymidine and found that as early as two days following the subtotal nephrectomy there was an increase in the glomerular mitotic index as well as an increase in the turnover of the cells forming the arterial wall. These findings suggest that a dysregulation of cell growth is an early event in the development of glomerulosclerosis.